Marcus in U.S. Pat. Nos. 4,618,531 and 4,794,038 disclosed new fiberballs of polyester fibers. Such fiberballs are often now referred to in the art by other terms, including "clusters"; this term "clusters" is sometimes used herein as Well as "fiberballs".
In the latter patent, Marcus disclosed the bonding of the fiberballs into molded products and other bonded products in which the polyester fibers became load-bearing fibers (sometimes called matrix fibers) that were bonded together by binder fibers. Such fiberballs have proved very useful commercially, and improvements and variations have been disclosed in U.S. Pat. Nos. 4,940,502, 4,818,599, 5,112,684, 5,154,969, 5,169,580, and 5,218,740, for example, the disclosures of which are hereby disclosed herein by reference, as are the disclosures of the aforesaid earlier Marcus patents.
It would be desirable, however, to produce such molded products with better resistance to compression/heat-set than have been available from materials available hitherto. For instance, some seating designers require cushioning materials to take an improved (i.e., numerically lower) set when tested according to ASTM 3574-D, the key test conditions of which require compression to 50% for 22 hours at 158.degree. F. (70.degree. C.) and allow 30 minutes of recovery time after release from such compression before the "set" is measured.